The cholesterol present in eggs has given rise to quite different dietary positions, which have evolved from rigorous restrictions in the past, to more lax and tolerant current recommendations with the intake of up to one egg a day in healthy people. What is surprising is that all these recommendations did not have much evidence behind them, since intervention trials on the subject were few and their results quite heterogeneous. The last meta-analysis on the relationship between egg intake and blood cholesterol was published in 2017 and it was a work that did not reach very conclusive results either, as I explained in this post. Therefore, it was not able to definitively settle the debate on this controversial relationship.
Fortunately, we have news. Just a few weeks ago, a new meta-analysis was published, “Association between Egg Consumption and Cholesterol Concentration: A Systematic Review and Meta-Analysis of Randomized Controlled Trials” (2020). This research, although it also focuses on intervention trials, has some differences from the previous one. In this case, only trials carried out with healthy people (without hypercholesterolemia or any other known pathology) have been taken into account and it includes some additional trials, one recent and four prior to the year 2000 (in the previous meta-analysis only works after the year 2000 were selected ).
After the appropriate searches and filters, the authors selected 17 trials, in which the changes produced in LDL and HDL cholesterol were compared, after eating one, two and up to three eggs a day with respect to the usual diet or with respect to not eating any. In the following table they summarized the characteristics of each of them, as well as their main results (click to enlarge):
At the end of the document we can find the final conclusions of the authors:
“(…) this is the largest meta-analysis looking at the impact of egg consumption on the LDL-c/HDL-c ratio among healthy subjects and reveals that greater numbers of eggs consumed per day may influence disease risks cardiovascular by increasing LDL-c and LDL-c/HDL-c ratio.In particular, high long-term egg consumption may lead to increased LDL-c/HDL-c and LDL-c ratios.However, Randomized trials with long-term follow-up are needed to ensure the association between egg consumption and human health.”
This does not seem good news, since a higher intake was associated with higher LDL values.
But let’s get to know the details and conclusions of the review better, because there are some pretty interesting aspects.
First, with regard to LDL (known as “bad”) cholesterol, the review concludes that daily egg intake results in an average increase of about 8 mg/dL, as shown in the figure below:
If we look at the results of each of the trials, we can see that in some studies there is a lot of interpersonal variability in the results; in some groups of people the changes were even negative (and they were classified as “hyper-responders” and identified with the letter “a” in the figure) and in other cases the cholesterol clearly increased (classified as “hyper-responders” and identified with the letter ” b”). In any case, an increase is mostly appreciated, so the final mean value was positive, staying at those modest 8 mg/dL
Regarding HDL (or “good”) cholesterol, the calculations show a small increase in its value (1.27 mg/dL), which was not statistically significant.
On the other hand, the variation of the LDL/HDL coefficient was analyzed, since since the relationship with cardiovascular disease of one is direct and that of the other is inverse, this figure helps to know the variation in the overall effect. The result of the meta-analysis showed that by eating eggs daily this coefficient increases on average 0.14:
Again we find wide interpersonal differences, “hyporesponders” (a) and hyperresponders (b).
If we continue reading the meta-analysis, we find more interesting aspects. The authors have segmented the results based on the number of eggs ingested per day, one, two or three units. And they present them in the following table:
If we analyze the figures, we see that in any of the three cases the LDL and LDL/HDL figures are positive, that is, they increase compared to not eating eggs, but there does not seem to be a “dose response”, something that was also detected in the 2017 meta-analysis. That is, eating more eggs does not increase cholesterol concentration to a greater extent: when comparing LDL values with one, two or three eggs a day (red box), the values practically do not change or present any trend. However, in the case of HDL (blue box) the values do seem to change, especially if 3 or more eggs are ingested daily; in that case the HDL increases clearly. And let’s remember that in principle HDL is associated with lower risk (although it is also true that these changes were not considered statistically significant).
So, paradoxically, the LDL/HDL ratio eating three eggs a day is somewhat lower than eating one egg a day, which “formally” could translate to a small reduction in risk (although it’s still higher than eating no eggs).
Interesting, right?
In any case, since cholesterol is not a “hard-point” (a direct indicator of disease or mortality), but an intermediate indicator, it is best to stick to the data: this meta-analysis indicates that in the case of healthy people and without hypercholesterolemia (personally I think the group of people with high cholesterol would be more interesting), eating one or more eggs a day compared to not eating any, increases LDL by an average value of 8.18 mg/dL. And eating three or more eggs a day slightly improves your LDL/HDL ratio compared to eating one or two.
Interpretation of the conclusions
When interpreting all these data and using them as a reference for clinical application, the recommended ranges in the official recommendations must be taken into account: For LDL, normal concentrations below 100 mg/dL are considered, normal-high of 100 -160 mg/dL and high from 160 mg/dL. Regarding HDL, it is recommended that it be above 35-40 mg/dL. And regarding the LDL/HDL ratio, a value less than 3 is usually recommended in men and less than 2.5 in women. Considering all this, we will be able to make the appropriate decisions with the help of our healthcare professional. And if you want to delve into the topic of cholesterol and health, you can consult this series of posts that I published on the subject.
But neither should these results be taken as absolute and definitive. If you read the results of the meta-analysis above, you’ll see that the conclusions are quite different. This is what can happen when the trial selection criteria are not the same, as has been the case. We must also take into account the aforementioned interpersonal variability, which has been known for some time and which has been reconfirmed in a subsequent trial (not included in the meta-analysis), “Differences in response to egg-derived dietary cholesterol result in distinct lipoprotein profiles while plasma concentrations of carotenoids and choline are not affected in a young healthy population” (2019). In this recent investigation, only one third of the subjects suffered an increase in their LDL cholesterol values after eating three eggs a day, while two thirds had no changes or these were reduced. In addition, the increase in LDL in this third of people was mainly due to the greater number of larger lipoprotein particles, which are associated with lower risk. And on the other hand, they did not suffer changes in the LDL/HDL ratio and improved in other interesting health indicators.
In any case, it is worth keeping a couple of things in mind, which I have already mentioned on several occasions.
The first is that the concentration of cholesterol in the blood is especially affected by the intake of saturated fats (1, 2), more than by dietary cholesterol. And, as I explained in detail in this previous post, a good part of the saturated fat we eat comes from ultra-processed foods. Therefore, since we are going to change something in the diet with the aim of reducing cholesterol, I think it would be a good idea to start by reducing this type of product. It is very likely that it will improve significantly in a short time and almost certainly other parameters will also improve, as I explained in this previous post, or as can be deduced from the recent review “Ultra-Processed Foods and Health Outcomes: A Narrative Review” (2020 ).
And second, it must always be taken into account that cardiovascular risk depends not only on LDL and HDL cholesterol, but also on other indicators and habits. That is why it is important to evaluate the risk taking into account all the factors, not only the one related to an isolated indicator, to make sure that what we can improve on the one hand, we do not spoil it on the other.
Eggs, cardiovascular disease and diabetes, plus meta-analyses
The authors found that some reduction in risk of coronary heart disease could be inferred from eating up to about 4 eggs per week, and some increase in risk of heart failure from this value, but given the diversity of results and the lack of robustness of the results, they concluded that “There is no conclusive evidence on the role of eggs in the risk of cardiovascular disease.”
The meta-analysis included the calculation of the following curves, showing the dose response in the relationship of four cardiovascular diseases (coronary heart disease, stroke, cardiovascular disease, and heart failure) and egg intake:
“The results of this updated meta-analysis do not show an overall association between moderate egg consumption and the risk of type 2 diabetes.”
The most curious thing about the study is that it once again brought to light the difference in the relationship between eggs and type 2 diabetes depending on the geographical origin of the studies. North Americans find a positive relationship, Europeans neutral and Asians negative, as can be seen in the image below:
